Tube fitting assemblies have been made in many different varieties and for many different uses. When corrosive fluids are to be conveyed by the tube and where high pressures are to be utilized, the prior art has generally used rather expensive tube fitting assemblies, constructed of expensive materials and with rather complex structures taking considerable time to manufacture the fitting as well as to assemble it.
One example of an adverse environment is the use of air conditioning assemblies in automobiles. The refrigerant used in the air conditioning units is rather corrosive and over a period of time has seemed to attack almost all packing or sealing material in the tube fitting assemblies, thus eventually causing leaks. Additionally the temperature range within the engine compartment of a modern automobile is as much as 200 degrees, from below zero degrees Fahrenheit to near 200 degrees Fahrenheit. Still further there is considerable vibration both from the engine and from road shocks. The combination of these factors has caused the use in automotive air conditioners of tube fitting assemblies which are rather expensive to manufacture and to assemble, in man hours of labor. Additionally there are millions of such automotive air conditioners made each year with many joints to be made for each air conditioner, and thus the industry is quite anxious to obtain a tube fitting assembly which is not only economical to use and manufacture, but also reliable so that expensive warranty work is not needed. Retrofitting a defective joint in an existing automobile out in the field is far more expensive than the total cost of all fittings on the entire automotive air conditioner in the first instance. Hence such industry is not interested in a cheap fitting which does not hold up under the severe conditions encountered.
The industry would also like to use aluminum tubing because it is light weight yet strong, but aluminum has traditionally been a difficult metal to join with another structure, one reason being that it is initially ductile but becomes rapidly work hardened and another reason is that the aluminum is subject to corrosion in the form of aluminum oxide which is a powdery yet an insulating material.
The prior art has known tube fittings with a flange or an annular bead, including those fittings where such bead acted against a resilient packing member. However, most of these were with reusable fittings of the two piece type such as an interthreaded nut and fitting connection. These are expensive to manufacture and time consuming to assemble. Where it is not necessary to be able to disassemble the fitting and reuse it, the prior art has known fittings which are assembled by an internal mandrel expanding the tube against a wall of the fitting. In this case the outwardly swaged tube is moved into engagement with a previously prepared aperture in the fitting which aperture takes several steps to prepare its shape properly to receive the tube. Then a further three or four step process is required to use a mandrel and die to outwardly swage the tube and finish the process of connecting the tube to the fitting. Accordingly the problem to be solved is how to construct a tube and fitting assembly and the method of assembling the same so as to overcome the economic and practical disadvantages of the prior art.